1. Field of the Invention
The present invention relates to a rotation detecting apparatus provided for detecting a rotational angle of a steering wheel of an automobile or the like.
2. Description of Related Art
There is a conventional rotation detecting apparatus described in, for example, JP-A-2000-283704 as shown by FIG. 17. FIG. 17 shows a rotation detecting apparatus integrated to a rotational connector apparatus 101 for electrically connecting a vehicle body side thereof and a steering wheel side thereof. That is, a rotation detecting apparatus 107 is provided between a lower housing member 103 and a lower cover member 105 of the rotational connector apparatus 101. The rotation detecting apparatus 107 is generally constituted by a drive gear 109, a driven gear 111, and a circuit board 113.
The drive gear 109 is constructed by a constitution of being cooperatively rotated in accordance with rotation of the steering wheel. The driven gear 111 is brought in mesh with the drive gear 109. The driven gear 111 is provided with a magnet 115 at a rotational center portion thereof. The magnet 115 includes a plane portion 117. The plane portion 117 is contiguously formed with an N pole and an S pole with a rotational center of the driven gear 111 as a boundary. The driven gear 111 is constructed by a constitution in which one face side thereof is rotatably supported by the cover member 105 and other face side thereof is brought into sliding contact with the circuit board 113. The circuit board 113 is provided with a magnetic reluctance element 119 opposed to the plane portion 117 of the magnet 115.
Further, when the drive gear 109 is rotated in accordance with steering of the steering wheel, the driven gear 111 is rotated cooperatively therewith. When the magnet 115 is rotated by rotating the driven gear 111, a magnetic field of the magnetic reluctance element 119 opposed to the plane portion 117 formed with the N pole and the S pole is changed and a reluctance value of the magnetic reluctance element 119 is changed in accordance with the change. An angle signal can be outputted to an external system by converting the change into the angle signal by an electronic circuit portion.
Therefore, a steering angle of the steering wheel or the like can accurately be detected without restricting an angle detecting range.
However, according to the above-described structure, one side face of the driven gear 111 is directly brought into sliding contact with the circuit board 113 and therefore, when the driven gear 111 is rotated, vibration or the like is brought about at the circuit board 113. Therefore, there is a concern of effecting adverse influence by the vibration on a soldered portion of a circuit element mounted to the circuit board 113 or the magnetic reluctance element 119 per se and there is a concern of deteriorating durability and detection accuracy of the apparatus.
It is an object of the invention to provide a rotation detecting apparatus capable of promoting durability and promoting detection accuracy of the apparatus by restraining vibration or the like from being brought about on a side of a circuit board when a driven gear is rotated.
A first aspect of the invention is characterized in that in a rotation detecting apparatus comprising a drive gear supported rotatably by a case having a cover and capable of rotating cooperatively with an object to be detected, a driven gear brought in mesh with the drive gear and capable of rotating cooperatively therewith, a magnet provided at a rotational center portion of the driven gear and having an end face portion contiguously formed with an N pole and an S pole, a circuit board arranged at the case, and a magnetic reluctance element attached to the circuit board and being opposed to the end face portion of the magnet and an electronic circuit part for converting an output signal of the magnetic reluctance element into a rotational angle signal, wherein the driven gear is rotatably interposed by the case and the cover and a constant distance is maintained between the end face portion and the magnetic reluctance element.
A second aspect of the invention is a method of fabricating the driven gear for the rotation detecting apparatus according to the first aspect of the invention and is characterized in that the case, the cover, the drive gear and the driven gear are formed by materials having substantially the same linear expansion coefficient.
According to first aspect of the invention, when the drive gear rotatably supported by the case having the cover is rotated cooperatively with the object to be detected, the driven gear brought in mesh with the drive gear can be rotated cooperatively therewith. The driven gear is provided with the magnet having the end face portion contiguously formed with the N pole and the S pole at the rotational center portion and the magnet can be rotated along with the driven gear. The case is arranged with the circuit board, the circuit board is provided with the magnetic reluctance element opposed to the end face portion of the magnet, a magnetic field of the magnetic reluctance element is changed by rotating the magnet, the reluctance value of the magnetic reluctance element is changed in accordance with the change and a signal can be outputted. The output signal of the magnetic reluctance element is converted into the rotational angle signal by the electronic circuit part provided to the circuit board and can be outputted to an external system as an angle signal.
Further, the driven gear is rotatably interposed by the case and the cover, the constant distance is maintained between the end face portion of the magnet and the magnetic reluctance element and therefore, when the driven gear is rotated, the driven gear is rotatably supported by the case and the cover and vibration or the like can be restrained from being brought about at the circuit board. Therefore, adverse influence by vibration can be restrained from effecting on a soldered portion of a circuit element and the magnetic reluctance element mounted to the circuit board, durability of the apparatus is promoted, and rotation can be detected accurately.
According to the second aspect of the invention, in addition to an effect of the first aspect of the invention, since the case, the cover, the drive gear and the driven gear are formed by materials having substantially the same linear expansion coefficient, even when temperature is changed to high temperature or low temperature, an influence is restrained from effecting on a relative relationship among the case, the cover, the drive gear and the driven gear and the detection accuracy equivalent to that at normal temperature can be ensured.